Summary of Work: The purpose of the methodology studies undertaken here is to prepare for large and/or definitive projects that examine the role of environmental toxicants in reproductive outcome. Methodology studies may address one part of a difficult investigation (such as validity of measurement), or they may be a pilot to highlight difficulties in a future study to be resolved, or they may be small studies using an accessible agent (rather than a rare environmental exposure) to elucidate mechanisms by which toxins affect reproductive health. This year methodology studies have focused on gestational age at the end of a pregnancy. Methodologic work in reproductive epidemiology using alcohol as a prototypical agent is ongoing. Another study in progress addresses definitions of gestational hypertension and how the diagnostic signs of this condition related to ICD codes in this and other countries.